This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In bacteria, the 450 kDa RNA polymerase (RNAP) holoenzyme, comprising the evolutionarily conserved catalytic core (subunit composition [unreadable]2[unreadable][unreadable]'[unreadable]) combined with the initiation-specific [unreadable] factor, directs transcription initiation. The primary [unreadable] factor, which only binds promoter DNA when complexed with RNAP, recruits RNAP to promoters containing conserved [unreadable]10 (TATAAT consensus for [unreadable]70) and [unreadable]35 (TTGACA) promoter elements. Once bound to the promoter in a closed complex (which is transient and relatively unstable), the holoenzyme spontaneously isomerizes to the transcription-competent open complex, in which the double-stranded DNA from the [unreadable]10 element downstream to the transcription start site is melted to form the transcription bubble. The [unreadable] factor plays a key role in open complex formation, in part by sequence-specific binding to the single-stranded, nontemplate strand of the -10 element within the transcription bubble. Our goal is to determine high-resolution crystal structures of complexes between [unreadable] and -10 element DNA to visualize this interaction critical for promoter melting.